In the current state of the art, the fluid control valve technology comprises on one hand so-called bellows valves, and on the other handle diaphragm valves. The bellows valves offer the advantages of outstanding flow coefficient and capability to work in low pressure down to a vacuum of 10-3 or 10-4 Torr. On the other hand, their main disadvantages are the problems of bellows fabrication due to variable mechanical profiles and to a substantial dead volume in the valve increasing significantly the valve draining time. Finally, said bellows valves have problems of gas contamination through particles coming from the bellows.
Diaphragm valves have a body in which fluid inlet and discharge pipes are provided, with the inlet pipe running into a face opposite which a diaphragm is mounted, which, through deformation, is capable of isolating or connecting up the fluid inlet and discharge pipes by sealing or not sealing the end of the fluid inlet pipe which makes up a seat for the diaphragm.
The major advantage of diaphragm valves is their simple fabrication compared to bellows valves since they can be produced through drawing, bending or cutting. In addition, they have a highly reduced dead volume and a better surface condition thus leading to a significantly lower contamination of the gas.
Offsetting those advantages, they have the problems of limited flow in the open position due to the diaphragm deflection and the possible penetration of moisture into the fluid lines and possible reaction to gasses such as HCl causing corrosion and chemical attack of the fluid lines. Finally, the questions of diaphragm/seat contact tightness in closed position crop up for this type of valve.
Various improvements were made on diaphragm valves, especially by choosing more precise round seats (Patent Application FR 91.07191) or defining diaphragm geometries designed to increase the valve flow in open position (Patent Application FR 91.07192).
Patent FR 0 530 947 describes a diaphragm valve in which the diaphragm has the shape of a spherical dome or cup.
The diaphragm is mounted in a chamber between a bearing of the latter and a ring which through deformation seals the circumferential edge of the dome making up the diaphragm.
The spherical dome shape of the diaphragm puts significant deformation strains on the diaphragm when switching from a position against the seat to a position away from the seat, which may cause rapid deterioration of the diaphragm.
U.S. Pat. No. 4,953,826 describes a diaphragm valve of the above-described type in which the deformable diaphragm is a planar disk which is deformed by an actuating head either curved or as a spherical portion.
The circumferential edge of the diaphragm is blocked between a chamber bearing and a sleeve.
This conformation of the diaphragm and of the actuating head can lead to a deformation of the diaphragm through punctures and deterioration.
The purpose of the invention is to propose a diaphragm valve which avoids such disadvantages.
Another purpose of the invention is to correct the problem of diaphragm valve automatic closing when a vacuum is created in the fluid line. As a matter of fact, in the most frequent case of planar diaphragm valves, just like in patent U.S. Pat. No. 4,953,826, when a vacuum is created in the fluid line, the diaphragm tends to get naturally deformed under the suction effect and to close by pressing against the seat.
The invention also aims at improving the tightness of the valve in relation to the outside environment.